1. Field of the Invention
The present invention relates to a bicycle hub, and more particularly to a protective structure for a bicycle hub.
2. Description of Related Art
Generally, a hub cassette 7 has a plurality of ribs 71 on the outer periphery of the hub cassette 7 for engagement with a sprocket 8, as shown in FIG. 9. The sprocket 8 is mounted around the hub cassette 7 and retained by the ribs 71. However, the ribs 71 may be worn easily for continuous riding since the sprocket 8 are generally harder than the ribs 71. At the same time, each rib 71 would be worn to produce a notch 72 which causes the sprocket 8 not to drive a bicycle hub effectively.
In order to solve the above problem, a conventional bicycle hub further comprises a metal sheet 9 attached to the rib 71, as shown in FIG. 10. Wherein, the rib 71 has a recess 73 in a top thereof for accommodating the metal sheet 9. The metal sheet 9 is harder than the sprocket 8. The metal sheet 9 is fixed to the rib 71 by a plurality of screws 10 so as to reinforce the structure of the hub cassette 7. However, the configuration of the recess 73 will increase manufacturing cost and the screws 10 may be loosened during riding.
Another type of bicycle hub is illustrated in U.S. Pub. No. 2013/0076112. In this bicycle hub, a driving socket has a plurality of ribs extending axially on the outer surface thereof and at least one protection unit located between two of the ribs and has an engaging portion. A cover is engaged with the engaging portion and has a cover face and two sidewalls to form an engaging groove. Specifically, the engaging portion has two transmission surfaces respectively located on two sides thereof and each transmission surface is gradually tapered toward the center of the driving socket. Each of the two sidewalls of the cover has an inclined surface corresponding to the respective transmission surface of the engaging portion for engagement between the engaging groove of the cover and the engaging groove. Furthermore, two sides of the engaging portion each has a positioning slot in the outer surface of the driving socket, wherein each sidewall of the cover has an extension engaged with the positioning slot to increase the contact area between the cover and the engaging portion. However, the configurations of the transmission surface and the positioning slot of the engaging portion will reduce the strength of the driving socket. Besides, the manufacturing processes of the engaging portion and the cover will increase manufacturing cost.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional bicycle hub.